1. Field of the Invention
The present invention generally relates to a method for increasing/reducing the band data rate of a ring-based network and a node apparatus such as an ADM (Add Drop Multiplexer) of the ring-based network.
2. Description of the Related Art
FIG. 1 shows an exemplary configuration of a ring-based network on which RPR operates on SDH/SONET. By forming bi-directional paths between each adjacent node apparatus (ADM apparatus) 1A-1D as shown in FIG. 1, bi-directional paths having uniform bandwidth through the node apparatuses 1A-1D can be obtained. An RPR ring is provided on the bi-directional paths.
FIG. 2 is a schematic diagram for describing an RPR function. In FIG. 2, the path connecting each node apparatus 1A, 1B is virtually a single band having plural SDH/SONET bands (paths) bundled together to form a VCG (Virtual Concatenation Group). This virtual band serves as an RPR bandwidth (i.e. an upper limit of an Ethernet (Registered Trademark) transmission path). With reference to FIG. 2, each node apparatus 1A, 1B includes an RPR processing part. The RPR processing part adjusts the amount of data (frames) inserted from an L2SW (Layer-2 Switch) to the RPR ring so that the data flowing into the RPR ring does not exceed an insertable data bandwidth (insertable data capacity) of the RPR ring (i.e. so that the total traffic (bandwidth) of the frames inserted by each node does not exceed the threshold of the RPR bandwidth). Furthermore, the RPR processing part monitors the frames passed from an adjacent node apparatus and the frames inserted from the L2SW, and transmits a control signal to an upper level apparatus (from which the frames are inserted) when the amount of frames flowing in the RPR ring exceeds the RPR bandwidth.
Meanwhile, there is another technology referred as an LCAS (Link Capacity Adjustment Scheme) function which serves to increase/reduce the bandwidth of a SDH/SONET network (add/delete members of a virtual concatenation group). FIG. 3 is a schematic diagram for describing the LCAS function. In a case where a transmission path 2a is currently used between the node apparatus 1A and the node apparatus 1B as shown in FIG. 3, another transmission path 2b is set (added) as a member of the VCG between the node apparatus 1A and the node apparatus 1B by using a control frame including information (overhead byte) referred to as H4 byte. After the transmission path 2b is set (added) as a member of the VCG, the increase of bandwidth is determined by monitoring abnormality thereof. The decrease of bandwidth is determined in a likewise manner.
It is to be noted that a member of the VCG refers to a unit for increasing/decreasing the bandwidth of the VCG.
In one related art case (Japanese Laid-Open Patent Application No. 2002-359627), there is disclosed a protection method employing LCAS in a case of failure and a ring apparatus using the protection method. In another related art case (Japanese Laid-Open Patent Application No. 2004-236205), there is disclosed a transmission apparatus which can separately perform ring switching at the SONET/SDH level and ring switching at the RPR level. In yet another related art case (Japanese Laid-Open Patent Application No. 2004-242194), there is disclosed an RPR network system which does not require, for example, a flag for identifying addition of a MAC (Media Access Control) address/capsulation of a frame.
Meanwhile, owing to the current spread/growth of Ethernet services, there are many occasions where the capacities of a ring-based network (e.g. ADM system) are adaptively changed in accordance with the user's needs, and there is a demand for achieving increase/decrease of physical bandwidth without affecting the traffic being carried. Nevertheless, the aforementioned related art cases have the following problems.    (1) For example, in a case of using the RPR function in an ADM system, the complicated operation of the RPR functions makes it difficult to increase/reduce the band data rate without affecting a prescribed service (e.g. Ethernet service). In order to achieve this, bandwidth (that is expected to be used) is additionally prepared before commencing the Ethernet service, for example, and the amount of data inflow is adjusted by a corresponding L2SW. With this method, however, the RPR function, which is meant to make efficient use of bandwidth, cannot be sufficiently utilized.    (2) Since the RPR function of, for example, an ADM system functions on a predetermined band (e.g. SDH), it is necessary to remove a path in order to increase the data rate of the predetermined band. For example, in a case of increasing a band of 150 Mps to a band of 300 Mbps, it is first necessary to remove (eliminate) the registration information of the band of 150 Mbps in order to increase the data rate to 300 Mbps. Such temporary interruption of service may cause adverse effects on the end user.    (3) The RPR function serves to insert a guaranteed amount of signals having predetermined priority corresponding to each interface within the extent of a designated band (e.g. SDH). However, in a case where the amount of traffic for the entire band is small, the RPR function can allow insertion of traffic exceeding the guaranteed amount. Furthermore, the RPR function constantly monitors a predetermined band (e.g. SDH) and the amount of packets inserted thereto and adjusts the amount of traffic (inserted packets). Therefore, in a case where the bandwidth of a given section is increased, the amount of traffic may increase only at the given section. Accordingly, when the inserted packets reach another section, the control for the incoming flow temporarily loses balance. This will initiate an automatic control for adjusting the amount of traffic control and eliminating transmission information. Thereby, packets (traffic) inserted from other interfaces are temporarily prevented from being inserted. Hence, in a case of increasing/decreasing the bandwidth between each section (interval) by using the LCAS function, the increase/decrease of bandwidth has an effect on the entire system. In other words, in a case where an RPR band is provided by bundling multiple bands (e.g. SDH) together, a frame is spontaneously transmitted to an increased/decreased band (e.g. SDH) since the RPR is unable to designate the band to which a frame is to be transmitted. This results in frame loss.    (4) The RPR function provides a logical ring formed by disposing a band (e.g. SDH) between sections that are physically connected by nodes (e.g. ADM), and uses the ring as a whole for adjusting the amount of traffic. Meanwhile, the LCAS function is a technology applied to, for example, SDH for increasing/decreasing the data rate of a path without causing any disconnection. It is, however, difficult to achieve cooperative operations between the RPR function and the LCAS function since the RPR function and the LCAS function operate in different layers. That is, the RPR function is a technology which uses a ring as a whole, and operates in a MAC layer (corresponding to Layer 2). The LCAS function is a technology for setting the bandwidth (e.g. SDH) between each node (technology standardized for changing the bandwidth between each section), and operates in a layer (corresponding to Layer 1) different from that of the RPR function. Although the LCAS function uses the H4 byte (physical layer) of, for example, SDH for controlling the increase/decrease of bandwidth, the LCAS function has no method for transmitting the control to Ethernet (MAC layer) and is unable to change the bandwidth of a ring as a whole. Even if the LCAS function were able to change the bandwidth of the ring as a whole, the starting node would be the terminal node (starting node=terminating node), and there would be no method for recognizing this relationship.
Accordingly, in a conventional ring-based network (e.g. ADM system) having an RPR function, it is difficult to increase/reduce the data rate without any disconnection of service. This is a complicated task for the user (operator), in which the user (operator) is to decide whether to 1) sacrifice the efficient use of bandwidth, 2) change the bandwidth along with disconnecting the line, or 3) ignore the temporary effect on the service.